Intracisternal or intrathecal glycine, taurine, or muscimol inhibit bicuculline-induced allodynia and thermal hyperalgesia in mice

Aim： To investigate the effects of GABA and glycine on analgesia in the central nervous system. Methods： Glycine, taurine, or muscimol was injected with bicuculline into the cistern magna or the lumbar subarachnoidal space in ICR mice. The effects on bicuculline-induced allodynia in a touch-evoked agitation test and on pain threshold index in a hot-plate test were assessed. Results： The dosages of the amino acids administered with bicuculline had no effect on motor behavior in conscious mice. Glycine or muscimol reduced bicuculline-induced allodynia regardless of the administration site, whereas intrathecal taurine reduced bicuculline- induced allodynia. Glycine, taurine, and muscimol all antagonized the effects induced by bicuculline in the hot-plate test, regardless of the administration site. Conclusion： Glycine, taurine, and muscimol were found to have anti-allodynic and anti-thermal hyperalgesic properties in vivo. These observations suggest an interaction between glycine and GABA receptors during the regulation of antinociception.